In order to reduce a load on the driver who drives the vehicle such as a passenger vehicle, a truck, and a bus, and to improve safety, a variety of driving assisting techniques for assisting the driver have been suggested and put into practical use. For example, Patent Document 1 discloses a vehicle steering device for improving a performance to avoid an obstacle by making a ratio of a steering amount of a steering wheel to an operational amount of a steering member smaller when visibility of an ambient environment is low.    Patent Document 1: Japanese Patent Application Laid-Open No. 2004-34740